What do you do with used shuttles?

Categorize the used shuttle, keep the still ok to fine shuttle, dump the bad one.

Use a used shuttle on warming up or drill.

Use a used shuttle for fun club. No need to expend more for shuttle as the games itself are not so technical but fun stroke.

If i had more than 1 or 2 full tube of used shuttle, give them the extra tube to this fun club. They love it. Free shuttle. Or leave it inside tube on the side of court, whoever rent the court & want it, they are free to take.

As for the tube itself, creativity is what it takes.
Made simple low table, use the tube as footing.
Cut it small & makes a pen/pencil storage.
Cut it extra small for trigonal clip box.
Or cut half & use it to keep my scissor, extra replacemnt grip, extra wrist band, & all other small badminton stuff there.